Between January, 1990, and December, 1994, 105 elderly patients(over the age of sixty) were referred to the Division of Nephrology at the Seoul National University Hospital as acute renal failure(ARF) (serum creatinine >1.7mg/dL, patients who had been diagnosed to have acute on chronic renal failure were excluded). To find out the characteristics of ARF in the elderly, we made a retrospective study of our data. Sufficient data for analysis were available in 101 of these. Among these patients, prerenal failure occured in 5% of the cases, ischemic ATN 34%, toxic ATN 11%, renovascular obstruction 5%, glomerular disease 5%, postrenal failure 15%. Dialysis was required in 31 patients(31%). Twenty four patients were treated by hemodialysis, it was carried out in 1 patient by the peritoneal route, and the other 6 patients were treated by CAVH. The most common indication was hypervolemia(77%). Twenty seven patients died during the period of acute renal failure. The most common cause of death was infection(15 patients), and the others were underlying diseases, pulmonary complications and cardiovascular complications. Oliguria, and chronic underlying disease were poor prognostic factors. There were significant differences between living and died group in APACHE II score(P<0.05). We conclude that ischemic ATN is a more common cause of ARF in the elderly than in the younger, and presence of oliguria and chronic underlying disease are poor prognostic factors.